N′-Acetyl-2-cyanoacetohydrazide (H2L1) and 2-cyano-N-(6-ethoxybenzo thiazol-2-yl) acetamide (HL2) ligands were used to synthesize [Cr(OAc)(H2L1)(HL2)]·2(OAc) and [Mn(H2L1)(HL2)]·Cl2·2H2O as mixed ligand complexes. All new compounds were analyzed by analytical, spectral, and computational techniques to elucidate their chemical formulae. The bidentate nature was suggested for each coordinating ligand via ON donors. The electronic transitions recorded are attributing to 4A2g(F) → 4T2g(F)(υ2) and 4A2g(F) → 4T1g(F)(υ3) types in the octahedral Cr(III) complex, while 6A1 → 4T2(G) and 6A1 → 4T1(G) transitions are attributing to the tetrahedral Mn(II) complex. These complexes were optimized by the density functional theory method to verify the bonding mode which was suggested via N(3), O(8), N(9), and N(10) donors from the mixed-ligands. Hirshfeld crystal models were demonstrated for the two ligands to indicate the distance between the functional groups within the two ligands and supporting the exclusion of self-interaction in between. Finally, the biological activity of the two mixed ligand complexes was tested by in silico ways as well as in vitro ways for confirmation. Three advanced programs were applied to measure the magnitude of biological efficiency of the two complexes toward kinase enzyme (3nzs) and breast cancer proliferation (3hy3). All in silico data suggest the superiority of the Mn(II) complex. Moreover, the in vitro assays for the two complexes that measure their antioxidant and cytotoxic activity support the distinguished activity of the Mn(II) complex.